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Over-The-Horizon Radar is a military radar system deployed by the United States in various places outside the continental USA. In recent years, interference assumed to be from these systems has been widely noted in the shortwave pirate and amateur radio bands, primarily around the area of 7 MHz. The sound of these systems on typical shortwave receivers sounds like a loud, wideband chirping, and older listeners liken the sound to the Russian woodpecker, a similar HF radar system of Soviet design.

See also